Process for controlling the horizontal movements of yarn carrier bars correlated with a predetermined distance between centres of the knitting needles in knitting machines

Abstract: It is described a process for controlling the horizontal movements of yarn carrier bars (3) correlated with a predetermined distance between centres of the knitting needles in knitting machines (1), through which it is possible to carry out the systematic adjustment of the yarn carrier bars in said knitting machines, in the observance of the working cycles, by procedures loaded into a central control unit (7) as wall as memories present in a microprocessor unit (9), associated with each of the stepping motors (10), for movement of the yarn carrier bars (3) according to tolerance values and parametric reference tables in connection with values relating to operating speed, step number detection and distance between centres of the needles, thereby giving rise, by comparison, to univocal risulting positioning values having definite accelerations and/or decelerations and angular speeds.

Description: The present invention relates to a process for controlling the horizontal movements of yarn carrier bars, correlated with a predetermined distance between centres of the knitting needles in knitting machines comprising the features recited in the preamble of claim 1. By working cycle it is intended an entire plurality of movements aiming at knitting any finished pattern to be made by the knitting machine. It is known that in fast knitting machines, such as crochet galloon looms, the formation of a manufactured article relies on the cooperation of different knitting members, such as needles, eye-pointed needles and tubular weft yarn guides or threading tubes, provided with a reciprocating movement synchronized in such a manner as to give rise to the interlacing of weft yarns engaged through the threading tubes, with the warp yarns passing through the eye-pointed needles and operatively engaging about the needles. The threading tubes are arranged in one or more rows disposed parallelly in side by side relation, each of which is supported by a corresponding yarn carrier bar through which the necessary reciprocating motions are transmitted so that the threading tubes may describe, by turns at each work stroke, a given trajectory selectively extending astride of one or more needles. To this end, the yarn carrier bars are engaged, at the respective opposite ends, to a pair of lifting plates simultaneously driven in an oscillatory motion by a vertical-movement mechanical linkage. In addition, operating on each of the yarn carrier bars is a second mechanical linkage giving the bar itself, and therefore the corresponding threading tubes, a horizontal oscillatory movement which, in combination with the above mentioned vertical movement, makes the threading tubes describe displacements according to a curved trajectory astride of the needles. By varying each time the width of the horizontal strokes of the individual yarn carrier bars, the threading tubes are induced to selectively ride over one or more needles concurrently with the formation of each knitting stitch, so as to give origin to the desired pattern or embroidery on the manufactured article. In knitting machines of the most usual conception, the reciprocating movement of the individual yarn carrier bars is achieved with the aid of the so-called "Glieder chains", consisting each of a plurality of suitably shaped cam elements, interlinked one after the other in an endless line. The cam elements of the individual Glieder chains, mounted on appropriate driving pulleys set in rotation, act on respective cam followers associated with the individual yarn carrier bars in order to cause the horizontal movement of the latter according to a width each time proportional to the lifting of the cam element coming into engagement with the cam follower. It is also known from DE-A-4215798 a warp knitting machine according to the preamble of independent claim 1 comprising at least one guide bar and one main shaft. The angular position of the main shaft and of the guide bar is determined by two absolute transmitters, each of which can provide a different signal value for each angular position of the main shaft and for each guide bar position. A continous displacement function is developed for the guide bar. Such a function relates each measured angular position of the main shaft with a position target value for the guide bar. A position control circuit controls a setting electrical linear motor that displaces the guide bar, avoiding dangerous collisions between the elements of the guide bars and other working parts of the machine. The Applicant has recently developed a device that, in place of said Glieder chains, utilizes a plurality of electric stepping motors operatively connected each with one of the yarn carrier bars. The selective operation of the stepping motors is managed by a programmable electronic control box into which any programs relating to the management of the motors themselves can be easily loaded, according to a work cycle suitable to obtain the desired pattern or embroidery in the manufactured article produced by the machine. In substance, the program loaded into the electronic control box contains all information relating to the extent of the stroke to be carried out, upon command of the respective motor, by each of the yarn carrier bars, at each knitting step. In order to give the control box the possibility of stopping each stepping motor the exact moment at which the yarn carrier bar has moved by the expected amount, a plate-like element is arranged on the output shaft of each of the stepping motors, which plate-like element is provided with optical references spaced apart from each other an amount corresponding to the distance between centres of the needles. Optical detectors interlocked to the control box and combined with each of the motors detect when the optical reference passes a predetermined reading point. Therefore the control box itself is capable of evaluating the number of needles ridden over by the threading tubes as a result of the movements of each yarn carrier bar so as to stop the horizontal movement of said bar at the appropriate moment. Each stepping motor is also equipped with a blocking mechanism adapted to intervene whenever the power supply to the knitting machine is broken, in order to ensure that the corresponding yarn carrier bar is stopped at a position adapted to enable the threading tubes to be inserted between the needles in the absence of mechanical interferences during the vertical strokes that are unavoidably carried out by the yarn carrier bars under inertia, before the knitting machine thoroughly stops. Each of these blocking mechanisms consists of a sector gear connected to the output shaft of the corresponding motor. This sector gear, the teeth of which are spaced apart an amount corresponding to the distance between centres of the needles, is designed to be engaged by a fitting wedge that, during the usual operation of the machine, is held by an electromagnet couteracting the elastic action of a spring. In the lack of current, the resulting de-energizing of the electromagnet causes the engagement of the fitting wedge between two consecutive teeth of the sector gear and, as a result, locking of the yarn carrier bar at a position adapted to avoid mechanical interferences between the threading tubes and the needles. Although the use of stepping motors with movement devices represents an important technical progress as compared to the use of Glieder chains, said movement devices have proved to be capable of further improvements under different points of view. For example, it has been found that detection of the optical reference passage before the reading point does not completely meet the requisite reliability and accuracy in the control of the stroke carried out by the individual yarn carrier bars. In fact, it is very difficult, above all at high operating speeds of the machine, to carry out stopping of the yarn carrier bar at a location sufficiently exact to avoid the risk of mechanical interference between the threading tubes and the needles, above all when a very high working fineness is required, that is when the distance between centres of the knitting needles is very reduced. In addition, in the case that, for any reason, one or more yarn carrier bars should undergo accidental shiftings that are not governed by the electronic control box, the control of the bar positioning would be permanently impaired as far as an operator intervenes and resets the entire movement device. This is essentially due to the fact that the electronic control box is exclusively capable of carrying out counting of the optical references passing before the reading points and does not have the possibility of executing any precise monitoring as regards the actual position of the yarn carrier bars in relation to the angular positioning of the output shafts of the stepping motors. In particular, it may happen that, due to vibrations or any other reason, an optical reference stopping at the reading point may slightly move back and, subsequently, reach again the reading point. The electronic control box would interpret such a circumstance as a displacement of the yarn carrier bar by an amount equal to the distance between centres of the needles whereas, as a matter of fact, the bar has not substantially moved. It is also to be pointed out that in the above described device operation of the stepping motors takes place at a predetermined and constant speed that, in order to reduce the risks of mechanical interferences when the machine is running at high speeds, must correspond to the highest speed that the motors can reach. As a result the mechanical members connected to the yarn carrier bar are greatly stressed even in cases in which said bar would have to carry out a limited displacement and consequently operation of the corresponding motor could take place at a reduced speed without involving risks of mechanical interferences between the knitting members. It will be also recognized that the plate-like elements carrying the optical references must be replaced every time the knitting machine is set up for executing workings having a fineness or stitch gauge different from the preceding one. Also the sector gears of the above mentioned blocking mechanisms must be replaced each time the working fineness is changed and, in addition, apart from that, the presence of said sector gears makes the device as a whole much more complicated. It is the main object of the invention to solve the above drawbacks by providing a process for controlling the horizontal movement of yarn carrier bars, correlated with a predetermined distance between centres of the knitting needles in knitting machines, at any step of the working cycle and also in case of emergency or sudden halt. The foregoing and further objects that will become more apparent in the course of the following description are achieved by a process for controlling the horizontal movement of yarn carrier bars, correlated with a predetermined distance between centres of the knitting needles in knitting machines as defined in the first claim and in the subsequent ones. Further features and advantages will be more fully understood from the detailed description of a preferred embodiment of a process for controlling the horizontal movement of yarn carrier bars correlated with a predetermined distance between centres of the knitting needles in knitting machines in accordance with the present invention, given hereinafter by way of nonlimiting example with the aid of the accompanying drawing in which the only figure (Fig. 1) is a diagrammatic view of a portion of a knitting machine equipped with stepping motors governed by a central control unit and each of which is associated with a respective microprocessor unit provided with a control firmware in accordance with the present invention. Referring to Fig. 1 a device for the horizontal movement of yarn carrier bars in a knitting machine has been generally identified by reference numeral 1. The device 1 is associated with a knitting machine, and more particularly a crochet galloon loom 2 and is arranged to act on one or more yarn carrier bars 3 (only one of which is shown) to cause the reciprocating motion of same. The yarn carrier bars 3, in known manner, carry a plurality of threading tubes, not shown, engaging respective weft yarns, not shown, and are operatively supported by at least two lifting plates 4 (only one of which is shown) slidably engaging said bars 3 according to a horizontal direction coinciding with the longitudinal extension of the yarn carrier bars themselves. Each lifting plate 4 is slidably guided in a vertical direction on a pair of guide rods 5 integral with a bed 6 of the knitting machine and the plates are simultaneously operated in a reciprocating motion along the rods by a mechanical linkage consisting of a connecting rod-crank assembly housed in the machine bed and not shown as known per se and conventional. The composition of the vertical oscillatory motion and horizontal oscillatory motion imparted to each yarn carrier bar 3, through the device 1, is such that the engaged threading tubes are driven in a reciprocating motion according to a substantially curved trajectory extending astride of one or more knitting needles (not shown in the drawing). The device 1 provides for the presence of a plurality of driving rods 8, each of which has one end 8a operatively linked to the end of one of the bars 3, as well as a second end 8b connected to an electric stepping motor 10 fastened, by a supporting bracket 10a, to a bearing framework 11 integral with the machine bed 6. Each stepping motor 10, known per se and conventional, lends itself to drive in rotation a respective output shaft 12 according to angular steps in succession having each a given angular width. The output shaft 12 of each stepping motor 10 is operatively connected to one of the driving rods 8 by an intermediate mechanical linkage 13 designed to transmit the horizontal movements to the corresponding yarn carrier bar 3 following the angular rotation imparted to the drive shaft itself. Such an intermediate linkage 13 preferably consists of a crank 14 keyed onto the output shaft 12 and operatively engaged to a connecting rod 15 connected to the driving rod 8. The interconnection between each connecting rod 15 and the respective driving rod 8 is achieved by means of a linking element in the form of a rod 16 slidably guided in a horizontal direction parallel to the movement of the yarn carrier bars 3 on a guide support 17 fastened to the framework 11. Still referring to the drawing, denoted by 9 is a plurality of microprocessor units interfacing in circuit with a central control unit 7, equipped with a microprocessor of the NEC 78K family and provided with an external key-operated control panel, not shown in the figure. The microprocessor units 9, assembled on each motor 10 coaxially with the output shaft 12 on the opposite side from the intermediate linkage 13, are cards provided with a microprocessor of the NEC 75X family having their own electrically programmable read only memories (EPROMs) and electrically erasable programmable read only memories (EEPROMs) associated in circuit, through connectors, to an absolute encoder carrying out the detection of the positioning steps of the respective stepping motor and sending a 10-bit signal (according to the known Gray code used in absolute encoders) to the respective microprocessor unit 9. The latter interprets the signal by means of a processing algorithm developed for the purpose. Each of said microprocessor units is also equipped with the whole interfacing circuitry, through a 485 serial line, with the central control unit 7 and, through optoisolators, with the respective stepping motor 10. Obviously a power circuitry for the respective supply from the mains is also provided. Also provided in the power circuitry are capacitors, not shown, that are charged during normal operation thereby giving rise to an energy storage which is available for use. Therefore the encoder of each microprocessor unit 9 carries out the detection of the angular position of the output shaft 12 of each stepping motor 10 with which it is associated. This enables the reference zero to be identified for each stepping motor 10. To this end, during the production test, before delivery to the final user, each of the yarn carrier bar of each knitting machine is brought to a predetermined position, for identifying the reference zero of each motor 10 through detection, by the respective encoder, of the angular position correspondingly taken by the output shaft. In short, associated with each motor 10 will be a given angle representing the respective reference zero. This reference zero is then sent, in the form of a signal relating to positioning, to the respective microprocessor unit 9 that will interpret it and store it into its own EEPROM. Both the microprocessor units 9 and central control unit 7 are respectively provided with a control firmware, developed in assembler language, in which reference tables of coded parameters have been logically scheduled, such as: operating speed of the knitting machine, number of angular steps that each motor must correspondingly carry out at each stroke of the yarn carrier bars, value of the distance between centres of the needles (stitch gauge), angular speed, acceleration, deceleration to be imparted to the output shafts of the individual stepping motors, as well as tolerance values and implementation procedures relating to the arranged working cycles. A remote unit, not shown in the drawing, is also provided and it consists of a personal computer, into which the working cycles designed to be then transferred to unit 7 have been preloaded in the form of Quick-Basic-developed programs. This transferring is carried out, in connection with the embodiment being described, by an infrared beam system providing for the use of a remote control means that draws the desired working cycles from the personal computer by means of an RS 232 serial line, stores them into random access memories (RAM) provided with a buffer storage and enables them to be transferred to unit 7 through an infrared sensor, provided in said unit 7. It is to be pointed out that the encoder referred to before and present in each microprocessor unit 9 is of the absolute type, enables a 360° counting, and enables a univocal identification, through the known 10-bit Gray code, of the positioning of the output shaft 12 of each stepping motor 10 which, in connection with the embodiment being described, carries out a complete revolution (360°) in 800 steps. For the above reason there is a degree of precision of each motor equal to 0.45, that is 27'. When an operator decides to execute a series of workings, he draws the working cycle or series of working cycles he needs from the remote site (personal computer) through the remote control means and through the remote control means he transmissively discharges that part of the programs that he has drawn from the personal computer. At this point the knitting machine is ready to execute the working cycle or cycles that are stored in its central control unit 7. The machine is started and thus all stepping motors 10 are brought to the respective first work position which can coincide with anyone of the angular positions detected by the respective absolute encoder, in connection with the established stitch gauge. In short, each stepping motor 10 will have its own zero, defined by a certain angular degree detected by the absolute encoder and corresponding to a mechanical zero which is the same for all of them. Listed in the EEPROM of each microprocessor unit 9 and sent from the central control unit 7 is a series of tolerance values of angular positioning within which each stepping motor must stop its output shaft at the end of each stroke imparted to the corresponding yarn carrier bar. Such tolerance values, in the form of numerical values referring to the tolerance margins of said angular positionings and processed on the basis of a corresponding algorithm of the control firmware, enable a continuous control of the steps that each motor 10 must carry out in order to move the respective output shaft 12 without exceeding, at the end of each stroke, the margins previously entered during the planning stage. In addition, according to the process, a series of boundary parameters can be defined, such as the operating speed of the knitting machine, the number of the angular steps that each motor 10 must execute, in observance of the selected working cycle, correspondingly with each stroke of the yarn carrier bar, as well as the stitch gauge value. Such boundary parameters are scheduled into parametric reference tables, logically correlated with each other, within said control firmware, based on a corresponding algorithm. Also provided by the process is the programming and mutual comparison of the angular speed, acceleration and decelaration values to be given to the output shafts of the individual stepping motors depending on said boundary parameters, in order to establish, at each moment of the selected working cycle, a single resulting positioning value of the respective motor 10 so that, at the end of the yarn carrier bar stroke, the insertion of the threading tubes between the knitting needles be ensure in the observance of the tolerance margins defined in the planning stage. The foregoing aims at achieving an actual and efficient control of the knitting machine without involving too important mechanical stresses and interferences between the threading tubes and knitting needles. The above process is embodied by a plurality of procedures of a control programm stored in the form of a firmware into memories of the central control unit 7 and microprocessor unit 9. More particularly, the above described program procedures are all disposed, as regards the control programming of stepping motors 10, in memories of the central control unit 7 and, as regards the parametric reference tables and tolerance values, in the memories of each microprocessor unit 9. The working cycles that are not used at the moment, are all loaded in the hard disk of the remote PC. On the contrary, the working cycle or cycles to be used are loaded in the EPROM of the central control unit 7. Advantageously, even in case of sudden break of the mains power, each stepping motor 10, supplied with the energy stored in the above capacitors, can residually stop and carry out a minimum number of steps, so that the corresponding yarn carrier bar is stopped when the respective threading tubes are in alignment with the spaces defined between the consecutive knitting needles. In particular, in case of break of the electric supply a procedure for stopping each stepping motor is automatically activated, after execution of a residual number of steps, at an angular speed, at an acceleration and/or deceleration that are exclusively dependent on the values of the boundary paramaters at the moment. Also provided are program selections (procedures) that in addition enable numbering of the axes, which means giving each axis a progressive numbering. The invention attains the intended purposes. In fact, by these software procedures, placed in the remote PC, the central unit 7 and the microprocessor unit 9, it is practically possible to control, step by step, the automation of any working cycle feasible through a knitting machine, by adjusting the movement of the yarn carrier bars in relation to the distance between centres of the knitting needles without being any longer bound to mechanical linkages and electromagnetic driving mechanisms, to the operator's choices, and to the necessity for each machine to have the whole execution program required. Obviously other parameter and circuit modifications are possible without departing from the scope of the invention as defined in the appended claims.

Claims: A process for controlling the horizontal movements of yarn carrier bars (3), correlated with a predetermined distance between the centres of the knitting needles in knitting machines, comprising the use of a plurality of motors (10) each operatively connected to a yarn carrier bar (3) for transmitting reciprocating movements having variable-width strokes to said bar, as well as a central control unit (7) managing working cycles carried out by said motors (10), said process comprising the following programming steps, carried out in microprocessor units (9) interacting with said central control unit (7), connected to the mains by a power circuitry and associated each with one of said motors (10): a) listing a series of tolerance values of positioning within which each motor (10) must stop its own output shaft (12) at the end of each stroke imparted to the corresponding yarn carrier bar (3); b) defining a series of boundary parameters; c) programming the values of the angular speed, acceleration and deceleration to be given to the output shafts (12) of the individual motors (10) depending on said boundary parameters characterized in that said motors (10) are stepping motors and in that the step of defining a series of boundary parameters comprises their scheduling into parametric tables identifying the operating speed of the knitting machine, the number of angular steps that each motor must execute correspondingly with each stroke of the yarn carrier bars (3), as well as the values of the distance between centres of said needles. A process according to claim 1, characterized in that in step a) a plurality of numerical values are prepared which refer to tolerance margins of angular positionings; suitably scheduled and logically correlated with each other so as to cause, in the observance of the selected working cycle, movements of the output shaft (12) of each stepping motor (10) according to a number of steps that does not exceed said margins as defined during the planning stage. A proces according to claim 1, characterized in that in steps b) and c) the boundary parameters are logically correlated with each other so as to associate them with the values of angular speed, acceleration and deceleration of the output shaft (12) of each stepping motor (10) in order to give rise to a positioning of the stepping motor shaft with a number of steps univocally defined according to a speed, acceleration and deceleration resulting from a comparison process between said values and each time depending on said boundary parameters at the moment. A process according to claim 3, characterized in that, as a result of a lack of power, stopping of each stepping motor (10) is provided after a residual number of steps has been carried out, at an angular speed, at an acceleration and subsequent deceleration that are exclusively dependent on the values of the boundary parameters at the moment. A process according to claim 3, characterized in that, as a result of a lack of power, stopping of each stepping motor (10) is provided after a residual number of steps has been carried out, at an angular speed and at a deceleration that are exclusively dependent on the values of the boundary parameters at the moment. A process according to claim 4, characterized in that the residual number of said steps is the lowest so that the corresponding yarn carrier bar (3) may arrange corresponding threading tubes for insertion of each of them between two consecutive needles. A process according to claim 4, characterized in that the residual number of said steps is achieved by supplying said stepping motors (10) with the energy stored, during normal operation, by capacitors provided in the power circuitry. A process according to claim 1, characterized in that the programming steps are program procedures stored into EPROMs assembled in the central control unit (7). A process according to claim 1, characterized in that the series of tolerance values referred to at point a), boundary parameters referred to at point b), and values referred to at point c) are scheduled into a program stored into PROMs assembled in the microprocessor units (9) of the stepping motors (10). A process according to claim 1, characterized in that detection of the number of steps executed by each stepping motor (10) is carried out by an absolute encoder associated with each of them. A process according to claim 10, characterized in that detection of the number of steps executed by each stepping motor (10) is carried out by an absolute encoder using a Gray code. A process according to claim 10, characterized in that detection of the number of steps executed by each stepping motor (10) is carried out by a ten-bit absolute encoder. A process according to claim 1, characterized in that each working cycle is transmitted to the knitting machine (1) by an infrared remote control means. A process according to claim 13, characterized in that each knitting machine (1) is provided with an infrared receiver for receiving the working cycles from the infrared remote control means.

Inventors: ZORINI LUIGI OMODEO, ZORINI, LUIGI OMODEO
Applicants: COMEZ SPA, COMEZ S.P.A.
Application year: 1994
Main classification: D04B27
IPC codes: D04B27